Deicing composition

ABSTRACT

A deicing composition is provided. The composition includes a potassium or sodium salt of a carboxylic acid and a lithium salt of a carboxylic acid or lithium nitrate, wherein the molar ratio of lithium to potassium or lithium to sodium is from 10 percent to 80 percent.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation application of U.S. application Ser.No. 12/625,672 filed on Nov. 25, 2009, issued as U.S. Pat. No. 7,943,057on May 17, 2011, which is a continuation of U.S. application Ser. No.11/533,568 filed on Sep. 20, 2006, now abandoned, which claims priorityto U.S. Provisional Application Ser. No. 60/719,624, filed Sep. 22,2005, the disclosures of which are incorporated herein by reference intheir entireties.

FIELD OF THE INVENTION

The present invention relates to deicing compositions suitable for useon any outdoor exposed concrete surfaces such as airport runways,taxiways and aprons, highways, sidewalks, parking lots, etc.

BACKGROUND OF THE INVENTION

Snow and ice on concrete pavements such as airport runways, roads,sidewalks, bridges and the like can lead to significant traffic andsafety issues. Thus, various compositions have been proposed to deicesuch concrete pavements. Historically, alkali and alkaline earthchlorides like sodium chloride, potassium chloride and calcium chloridehave been used. These compounds while effective and relativelyinexpensive are; however, very corrosive with respect to metals likeiron, copper, aluminum, and the like. In addition, such chlorides can beharmful to the environment. Thus, while these materials may beacceptable in some applications, chloride-bearing deicers are notsuitable for concrete surfaces, particularly those used by aircraft.Glycol-based formulations, urea-containing formulations andmethanol-containing formulations have also been suggested. Theseformulations, however, can be toxic, corrosive, and some are highlyflammable.

To overcome these problems, it has been suggested to use sodium orpotassium acetate or formate solutions. See, for example, U.S. Pat. No.5,064,551 to Smith et al. and U.S. Pat. No. 5,350,533 to Hubred et al.Such acetates and formates tend to be more environmentally friendly andless corrosive to metal objects. These compositions; however, tend tocause cracking and deterioration on the surface of the concretestructure and within the concrete matrix.

A major cause of this concrete deterioration is due to the alkali-silicareaction (ASR). Stark, D., Morgan, B., Okamoto, P. and Diamond, S.“Eliminating or Minimizing Alkali-Silica Reactivity.” SHRP-C-343,Strategic Highway Research Program, National Research Council,Washington, D.C., 1993, 226 p. ASR, in addition to cracking, can causedeleterious expansion and surface spalling. ASR is a condition thatexists in concrete because of four main factors: reactive silica, whichis supplied by the aggregates in the concrete; a high pH in the poresolution, high enough to begin to dissolve whatever species of reactivesilica is present (different thresholds for different species);significant sodium and potassium ions to combine with the dissolvedsilica and form reactive gels (ASR reaction product); and, sufficientmoisture to first enable the reactions to proceed at all (i.e.,providing a medium for ion transport), and secondly, to supply moistureto the gels which will absorb it and expand.

ASR can weaken the ability of concrete to withstand other forms ofattack. For example, concrete that is cracked due to this process canpermit a greater degree of saturation and is therefore much moresusceptible to damage as a result of “freeze-thaw” cycles. Similarly,cracks in the surfaces of steel reinforced concrete can compromise theability of the concrete to keep out salts when subjected to deicers,thus allowing corrosion of the steel it was designed to protect. ASR canalso cause the failure of concrete structures. Prior attempts to controlASR include, for example, using cement with very low alkali content,non-reactive aggregate, and pozzolanic materials such as fly ash, silicafume, ground blast granulated furnace slag, zeolite minerals, thermallyactivated clay, and the like.

Lithium-based compounds have been shown to be effective in ASRinhibition by introducing these chemicals into concrete or mortar mixcompositions. W. J. McCoy and A. G. Caldwell, “New Approach toInhibiting Alkali-Aggregate Expansion,” J. Amer. Concrete Institute,22:693-706 (1951). However, this requires introducing the lithium-basedcompounds in the concrete or mortar mixture and does not address theproblem of controlling or remediating ASR in existing hardenedstructures or the deicing issues.

Thus, a need has been identified for a composition that is an effectivedeicer and that significantly reduces deleterious ASR effects of sodiumand potassium chloride or acetate compositions.

SUMMARY OF THE INVENTION

In an embodiment of the invention, a deicing composition comprising apotassium or sodium salt of a carboxylic acid and a lithium salt of acarboxylic acid or nitrate is provided. In one embodiment, the molarratio of lithium to potassium or lithium to sodium is from 10 percent to80 percent. Suitable carboxylic acids include formic, acetic, propionic,glycolic and lactic acid.

In another embodiment, in applications where corrosion concerns do notrestrict their use, the incorporation of significant ratios of lithiumcompounds along with metal (e.g., sodium, potassium, calcium, and/ormagnesium) halide salts can moderate ASR-aggravating effects that wouldotherwise ensue with the use of non-lithium-bearing compositions. Themolar ratio of lithium to the metal of the salt is from 10 to 80percent.

Additional embodiments of the present invention provide methods ofapplying the compositions of the above embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The above objects and advantages of the present invention will becomemore apparent by describing in detail embodiments of the presentinvention with reference to the attached drawings in which:

FIGS. 1-4 are graphs of expansion in percent versus age in days for adeicing composition having a Li/K ratio of 0.19 and for variousconcentrations of potassium acetate and concrete aggregates.

FIGS. 5-7 are graphs of expansion in percent versus age in days for adeicing composition having a Li/K ratio of 0.74 and for variousconcentrations of potassium acetate and various concrete aggregates.

DETAILED DESCRIPTION OF EMBODIMENTS ACCORDING TO THE INVENTION

The present invention will now be described more fully herein withreference to the accompanying drawings, in which embodiments of theinvention are shown. This invention may, however, be embodied in manydifferent forms and should not be construed as being limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete and will fully conveythe concept of the invention to those skilled in the art.

The terminology used in the description of the invention herein is forthe purpose of describing particular embodiments only and is notintended to be limiting of the invention. As used in the description ofthe embodiments of the invention and the appended claims, the singularforms “a”, “an” and “the” are intended to include the plural forms aswell, unless the context clearly indicates otherwise.

Unless otherwise defined, all terms, including technical and scientificterms used in the description of the invention, have the same meaning ascommonly understood by one of ordinary skill in the art to which thisinvention belongs. All publications, patent applications, patents, andother references mentioned herein are incorporated by reference in theirentirety.

It will be further understood that the terms “comprises” and/or“comprising,” when used in this specification, specify the presence ofstated features, steps, operations, elements, and/or components, but donot preclude the presence or addition of one or more other features,steps, operations, elements, components, and/or groups thereof.

Moreover, it will be understood that steps comprising the methodsprovided herein can be performed independently or at least two steps canbe combined. Additionally, steps comprising the methods provided herein,when performed independently or combined, can be performed at the sametemperature or at different temperatures without departing from theteachings of the present invention.

The deicing composition of the present invention comprises a potassiumor sodium salt of a carboxylic acid and a lithium salt of a carboxylicacid or an alkali metal nitrate. Suitable carboxylic acids includeformic, acetic, propionic, glycolic, and lactic acid, or mixturesthereof Suitable alkali metal nitrates include lithium nitrate.

Control of the amount of potassium or sodium ions to lithium ions is oneattribute of the present invention. This amount is often expressed interms of molar ratio. The amount of lithium necessary for preventingdeleterious expansions from ASR is related to the alkali loading of theconcrete, and is usually calculated based on the alkali loading of theconcrete supplied by the Portland cement component of the concrete. Inone embodiment, the molar ratio of lithium to potassium is from 10percent to 80 percent.

The amount of the potassium or sodium salt of a carboxylic acid may be0.1 to 95 percent by weight, and often is 27 to 86 percent by weight.The amount of the lithium salt of a carboxylic acid may be 0.1 to 95percent by weight, and often is 14 to 76 percent by weight.

In deicing situations wherein corrosion is not as big of a concern, thedeicing composition can comprise a metal chloride and a lithium salt ofa carboxylic acid or a lithium nitrate. Exemplary metals includepotassium, sodium, magnesium, and calcium. Again, the lithium to metalratio is from 10 percent to 80 percent.

An example of a deicing solution would be an aqueous solution that was4.5 molar in potassium acetate and 1.7 molar in lithium nitrate. Anotherexample of a deicing solution would be an aqueous solution that was 3.7molar in potassium acetate and 2.8 molar in lithium acetate, informulations with or without corrosion inhibitors. Another example wouldbe an aqueous solution that was 4.5 molar in potassium acetate and 2.0molar in lithium acetate, in formulations with or without corrosioninhibitors. Another would be an aqueous solution that was 4.0 molar inpotassium acetate, 1.0 molar in calcium acetate, and 1.5 molar inlithium acetate, in formulations with or without corrosion inhibitors.Another example of a solid (powder, granulated, or pelletized)formulation would be a blend of 2 parts sodium acetate trihydrate and 1part lithium acetate dihydrate, with or without added corrosioninhibitors. Another example of a solid formulation would be a blend of 4parts sodium acetate trihydrate and 1 part lithium acetate dihydrate,with or without added corrosion inhibitors. Another example of a solidformulation would be a blend of 4 parts calcium magnesium acetate (CMA)and 1 part lithium acetate dihydrate, with or without added corrosioninhibitors. Another example of a solid formulation would be a blend of 3parts sodium formate and 2 parts lithium formate monohydrate, with orwithout added corrosion inhibitors. Another example of a solidformulation would be a blend of 3 parts sodium formate and 1 partlithium formate monohydrate, with or without added corrosion inhibitors.Another example of a solid formulation would be a blend of 3 partssodium chloride and 1 part lithium chloride, with or without addedcorrosion inhibitors.

Additionally in one embodiment involving aqueous solutions based onacetate salts, the percent solids amount is controlled. In oneembodiment, the weight percent solids of the deicing composition is 40percent to 55 percent. In another embodiment, the weight percent solidsis 45 to 49 percent. The weight percent solids is controlled in order tomaintain a sufficiently low freezing point for liquid deicers. Statedotherwise, the amount is controlled to avoid adversely affecting theeutectic point of the salt. Under this disclosure for use on airfieldsunder current typical specifications (SAE AMS 1435A) for airfields, theminimum solids content would be 46% or higher for combinations oflithium and potassium actetate in solution.

The deicing composition may include corrosion inhibitors. Suitablecorrosion inhibitors may include zinc, antimony, phosphates, phosphonicacid derivatives such as 1-hydroxyethylidene diphosphonic acid (HEDP),nitrates, manganese, cadmium, nickel, cobalt, tin, aluminum, alkylmolybdates, amines, carbohydrates, gluconates, citrates, silicates, andtriazoles, such as tolyltriazole salts, and mixtures thereof The amountof corrosion inhibitor is from 0.0 to 5 percent by weight.

The compositions of the invention also advantageously include one ormore surface active agents. As used herein, the term “surface activeagent” refers generally to agents capable of reducing the surfacetension of liquids. Such agents are also known generally in the art alsoas surfactants. Various surface active agents can be used in thecompositions of the invention, including cationic, anionic, nonionic,and amphoteric surfactants, and mixtures thereof Exemplary surfactantsinclude fluorocarbon anionic, cationic and nonionic surfactants, suchas, but not limited to, amine perfluoroalkyl sulfonates, potassiumfluorinated alkyl carboxylates, fluorinated alkyl quaternary ammoniumiodides, fluorinated alkyl esters, and the like useful as surface activeagents. Useful surfactants include fluorocarbon anionic, cationic andnonionic surfactants commercially available from 3M as the Fluorad®series of surfactants and the Dowfax® surfactants available from DowChemical.

The deicing composition is applied to the concrete surface usingconventional techniques. An exemplary technique is spraying. The methodused to apply the composition to the concrete surfaces is not believedcritical, so long as the deicing composition contacts the surface of thestructure for time sufficient to allow deicing to occur.

The concrete surfaces to be treated include airfield runways, aprons,taxiways; roadways, sidewalks, bridges, etc, namely virtually alloutdoor-exposed concrete surfaces that receive vehicular or pedestriantraffic. Exemplary concrete compositions are cement, aggregates, water,and conventional additives such as air-entraining, water reducing,accelerating and retarding admixtures, corrosion inhibitors, and thelike. As used herein, the term “cement” refers to, but is not limitedto, hydraulic and alite cements, such as Portland cement; blendedcements, such as Portland cement blended with fly ash, blast-furnaceslag, pozzolans, and the like, and mixtures thereof masonry cement; oilwell cement; natural cement; alumina cement; expansive cements, and thelike, and mixtures thereof Portland cements include cements such asdescribed in ASTM C150 Type I and IA, Type II and IIA, Type III andIIIA, Type IV, and Type V. The term also includes cements blended withASTM C311 defined pozzolanic materials such as fly ash, raw and calcinednatural pozzolans, ASTM C989 defined ground granulated blast furnaceslag, ASTM C1240 defined silica fume materials, metakaolin, and thelike. Suitable aggregates include limestone, rhyolite, argillite, andquartzite.

The present invention will be further illustrated by the followingnon-limiting examples.

EXAMPLES

To demonstrate the effectiveness of the lithium portion of the deicercomposition, the following experiments were conducted Mortarsincorporating four different aggregates were cast into ASTM C 1260-typebars using ASTM C150 Type 1, high alkali (0.82% Na₂O_(eq)) cement. Theaggregate types were a limestone (“L”), a rhyollite (“R”), an argillite(“A”), and a quartzite (“Q”), and all have demonstrated deleterious ASRreactions in actual concrete structures in the field. Controls of 50percent (6.4M) potassium acetate were used, and the mortar bars werestored in these solutions, and duplicates in the solutions describedbelow, at 80° C. FIGS. 1-4 show the percent expansion versus age datafor the mortar bars stored in the various concentrates (1M, 2M, 3M,6.4M) of potassium acetate and with solutions incorporating lithiumnitrate at a molar ratio of Li/K of 0.19. FIGS. 5-7 show the percentexpansion versus age data for the mortar bars stored in the variousconcentrates (1M, 2M, 3M) of potassium acetate and with solutionsincorporating lithium nitrate at a molar ratio of Li/K of 0.74. Percentexpansion in these conditions above 0.1 percent at 14 or 28 days isindicative of deleterious ASR in the mortars. For most aggregates shownhere, the lower 0.19 Li/K ratio was sufficient to control the expansionin these test conditions, which is far lower than what is normallyassumed to be a necessary amount of lithium to control the expansion,and is one of the teachings of this patent. For very highly reactiverhyolitic aggregates such as the one shown here, significantly higherLi/K ratios are necessary in the more concentrated potassium acetateenvironments, and these approach the upper limit of a 0.80 Li/K molarratio.

Having thus described certain embodiments of the present invention, itis to be understood that the invention defined by the appended claims isnot to be limited by particular details set forth in the abovedescription as many apparent variations thereof are possible withoutdeparting from the spirit or scope thereof as hereinafter claimed.

That which is claimed:
 1. In a deicing composition that can cause ASRdamage to concrete being deiced, the improvement comprising adding alithium salt of a carboxylic acid or a lithium nitrate at a weightpercent solids level such that the freezing point of the deicingcomposition is maintained and the deicing composition's eutectic pointis not adversely affected.
 2. The deicing composition of claim 1,wherein the weight percent solids of the deicing composition is 40percent to 55 percent.
 3. The deicing composition according to claim 1,wherein the carboxylic acid is selected from the group consisting offormic, acetic, propionic, glycolic, and lactic acids, and mixturesthereof.
 4. A deicing composition according to claim 1 furthercomprising a corrosion inhibitor.
 5. A deicing composition according toclaim 4, wherein the corrosion inhibitor is a phosphate or a nitrate.